Closing the dimethyl sulfide budget in the tropical marine boundary layer during the Pacific Atmospheric Sulfur Experiment

Error analysis of the various terms in the DMS budget indicate that chemical losses acting on time scales of up to 110 h can be inferred with this technique. On average, photochemistry accounted for ~7.4 ppt hr ⁻¹ loss rate for the seven daytime flights, with an estimated error of 0.6 ppt hr⁻¹. The loss rate due to expected OH oxidation is sufficient to explain the net DMS destruction without invoking the action of additional oxidants (e.g., reactive halogens.) The observed ocean flux of DMS averaged 3.1 (±1.5) μmol m⁻²d⁻¹, and generally decreased throughout the sunlit hours.

Over the entire mission, the horizontal advection contribution to the overall budget was merely -0.1 ppt hr⁻¹, indicating a mean atmospheric DMS gradient nearly perpendicular to the east-southeasterly trade winds and the chlorophyll gradient in the equatorial upwelling ocean. Nonetheless, horizontal advection was a significant term in the budget of any given flight, ranging from −1.2 to 2.5 ppt hr⁻¹ , indicating a patchy and variable surface seawater DMS distribution, and thus needs to be accounted for in budget studies.